This project seeks to isolate and characterize the principal protein and lipid components of chick embryonic plasma membranes of lens-epithelial cells and lens-fibers, to determine whether the membrane composition changes during lens cell differentiation and to follow any changes which occur in the rates of synthesis or degradation of membrane components as a function of developmental time. Eight proteins have been isolated from highly-purified plasma membranes from lens fibers of 15-day-old chick embryos. One of these has the subunit molecular weight of delta-crystallin, the predominant protein of embryonic chick lens fibers.